Skin Breathers

At birth, the Julia Creek dunnart, a mouselike creature from northeast Australia, is less than two-tenths of an inch long and weighs a scant .0006 ounce. While in its mother's pouch, the tiny marsupial has such poor control over its respiratory muscles that it simply cannot breathe in and out. Physiologist Jacopo Mortola of McGill University has discovered that the dunnart survives by breathing through its skin, the only mammal known to do so.

"Gas exchange through the skin was thought impossible in mammals," Mortola says, because they have thick skin to maintain high body temperatures and reduce water loss.